An infrared imaging device is capable of remotely measuring the temperature of an object, and is used as a surveillance camera, or the like, for detecting a human or detecting a car.
FIG. 8 is a diagram illustrating an exemplary configuration of a conventional infrared imaging device (described in Japanese Laid-Open Patent Publication No. 5-302855). The configuration of FIG. 8 is used for the purpose of calibrating the relationship between the output signal and the temperature.
In FIG. 8, the characteristics of an infrared detector 1010 (object temperature versus brightness table) as illustrated in FIG. 9 are pre-stored in temperature characteristic correction means 1050. Each of graph curves 1210, 1220, 1230 and 1240 of FIG. 9 represents a relationship between an object temperature T and an output voltage Ei of the infrared detector 1010, with temperatures T1, T2, T3 and T4 in the vicinity of the infrared detector 1010 being used as parameters.
Temperature measurement means 1080 measures a temperature Tx in the vicinity of the infrared detector 1010. Temperature characteristic correction means 1050 uses the temperature Tx and the characteristics of FIG. 9 to obtain the object temperature T from the output voltage Ei of the infrared detector 1010. Assuming that T2<Tx<T3, the temperature characteristic correction means 1050 creates a characteristic curve 1250 by interpolating the graph curves 1220 and 1230, respectively corresponding to the temperatures T2 and T3, and converts the output voltage Ei of the infrared detector 1010 into the object temperature T by using the characteristic curve 1250.
FIG. 10 is a diagram illustrating another exemplary configuration of a conventional infrared imaging device (described in Japanese Laid-Open Patent Publication No. 10-111172).
In FIG. 10, optical systems 1310 and 1320 cause the infrared image of an object 1330 to form an image on an infrared detector 1340. Each of a reference heat source A 1350 and a reference heat source B 1360 is a heat source using a Peltier element, and the temperature thereof is variable and controlled by controllers 1440 and 1450, respectively.
The infrared imaging device illustrated in FIG. 10 images the target object during an effective scanning period, while it images the reference heat source A 1350 and the reference heat source B 1360 during an ineffective scanning period. Average value calculation means 1370 calculates the average value of the output of the infrared detector 1340 during the effective scanning period. Reference heat source A output calculation means 1380 calculates the average value of the output of the infrared detector 1340 while imaging the reference heat source A 1350 during the ineffective scanning period, whereas the reference heat source output calculation means 1390 calculates the average value of the output of the infrared detector 1340 while imaging the reference heat source B 1360 during the ineffective scanning period, and median value output means 1400 outputs the median value of these calculation results. A subtractor 1410 subtracts the output of the median value output means 1400 from the output of the average value calculation means 1370, and an adder 1420 adds a predetermined temperature difference ÄT to the subtraction result and provides the obtained value to the reference heat source A controller 1440, whereas a subtractor 1430 subtracts the temperature difference ÄT from the subtraction result and provides the obtained value to the reference heat source B controller 1450. The controllers 1440 and 1450 perform a feedback control so that the subtraction result of the subtractor 1410 is zero, i.e., the output of the average value calculation means 1370 and the output of the median value output means 1400 are equal to each other.
With such a control, even if the scene being imaged changes, the temperatures of the reference heat source A 1350 and the reference heat source B 1360 change according to the average value of the temperature of the obtained image, and are always controlled within a predetermined temperature range (average value±Ät). Correction means 1460 obtains a correction coefficient used for correcting output variations, based on the output of the infrared detector 1340 while imaging the reference heat source A 1350 and the reference heat source B 1360 during the ineffective scanning period. In this way, a temperature calibration suitable for the temperature range to be measured is realized.
FIG. 11 is a diagram illustrating another exemplary configuration of a conventional infrared imaging device (described in Japanese Laid-Open Patent Publication No. 10-142065). The configuration of FIG. 11 is used for the purpose of eliminating two-dimensional output variations.
In FIG. 11, first shutting means 1510 is provided for shading correction, and second shutting means 1530 is provided for inter-pixel output variation correction. During an imaging operation, the first and second shutting means 1510 and 1530 are open, whereby an infrared radiation coming through an optical system 1520 forms an image on an infrared detector 1540.
The first shutting means 1510 is closed by a control means 1560 once in every 30 seconds so as to shut off the infrared radiation. In this state, inter-pixel output variation correction means 1550 determines a shading correction value based on the output of the infrared detector 1540. On the other hand, the second shutting means 1530 is also closed by the control means 1560 once in every 30 seconds so as to shut off the infrared radiation. In this state, the inter-pixel output variation correction means 1550 determines a sensitivity correction value based on the output of the infrared detector 1540.